This invention relates to a magnetic head used for recording and/or reproducing information signals, such as audio or video signals, for a magnetic recording medium, such as a magnetic tape, or data signals, handled in an information processing unit, such as a personal computer.
Up to now, a metal-in-gap (MIG) type magnetic head has been used as a magnetic head for exchanging the information with a magnetic recording medium, such as a magnetic tape.
The MIG type magnetic head is formed by abutting and bonding a pair of magnetic core halves, formed of ferrites, to each other. With this magnetic head, a magnetic gap is formed on abutment surfaces of the paired magnetic core halves abutted and bonded to each other. Two track width controlling grooves are formed in each of the paired magnetic core halves forming the magnetic head. These track width controlling grooves control the track width of the magnetic gap when the paired magnetic core halves are abutted and bonded together to form the magnetic gap. In the MIG type magnetic head, a magnetic metal film is formed in the magnetic gap and in the track width controlling grooves.
Towards one side, for example an overwrite side, of the magnetic gap of the MIG type magnetic head, lying towards a recording track previously formed by sequentially recording information signals on the magnetic tape, there is formed a groove extending parallel to the tape running direction. This groove is provided for preventing the so-called side erasure from occurrence. This side erasure is caused by the unneeded stray magnetic flux from being produced from a track edge corresponding to one end of the magnetic gap to disturb the pattern of the recording track recorded on the magnetic tape.
Referring to FIG. 1, a magnetic head, formed by abutting and bonding a pair of magnetic core halves to each other, is prepared by abutting a first magnetic core half 10 and a second magnetic core half 20 to form a head block 1, by applying preset machining operations to this head block 1 and by slicing the head block 1 into plural discrete magnetic heads.
FIG. 1 shows the head block 1 obtained on abutting the two paired, that is first and second magnetic core half blocks 10 and 20, and on machining the resulting product. The head block 1, shown in FIG. 1, is formed by abutting and bonding the first and second magnetic core half blocks 10 and 20, and is shown in a state prior to severing the block into discrete plural magnetic heads. FIG. 1 shows the head block, yet to be severed into discrete plural magnetic heads, looking from the tape sliding surface formed on each discrete magnetic head.
In the head block 1, formed on abutting the first and second magnetic core half blocks 10 and 20 to each other, there is formed as magnetic gap g in the abutment surface of the first and second magnetic core half blocks 10 and 20, as shown in FIG. 1.
In the first magnetic core half block 10, forming the head block 1, there are formed a first track width controlling groove 11 and a second track width controlling groove 12 for controlling the track width of the magnetic gap g. In the second magnetic core half block 20, there are similarly formed a first track width controlling groove 21 and a second track width controlling groove 22 for delimiting a track width Tw of the magnetic gap g along with the first and second track width controlling grooves 11, 12 formed in the first magnetic core half block 10.
The track width Tw of the magnetic gap g, formed in the head block 1, is controlled to high accuracy by the first and second track width controlling grooves 11, 12 and 21, 22 formed in the first and second magnetic core half blocks 10 and 20 abutted and bonded to each other, respectively. The reason is that the width of the abutment surfaces of the first and second magnetic core half blocks 10 and 20 delimiting the magnetic gap g is precisely controlled by the first and second track width controlling grooves 11, 12 and 21, 22 provided in the first and second magnetic core half blocks 10 and 20, respectively.
The head block 1 is sliced along first and second parallel slicing lines E3, E4 on both sides of the magnetic gap g to sever a magnetic head 50. The surface of the so severed magnetic head 50, in which is formed the magnetic gap g, serves as a sliding surface 51 on which slides the magnetic tape. The magnetic tape is run in sliding contact with a sliding area on the sliding surface 51, indicated by dotted lines E1 and E2 extending parallel to each other.
In the sliding surface 51 of the magnetic head 50, severed from the head block 1, there is formed a groove 30 for inhibiting side erasure. This groove is formed towards one end of the magnetic gap g for extending parallel to the tape running direction. The groove 30 is formed to affect a portion of one end of the magnetic gap g.
On both sides of the magnetic gap g of the magnetic head 50, severed from the head block 1, and in the first and second track width controlling grooves 11, 12, 21, 22, there are provided metal magnetic films. These metal magnetic films, provided to the magnetic head 50, form magnetic channels for the magnetic flux emanated from the magnetic head. In the groove 30 is charged e.g., glass.
With the magnetic head 50, including the groove 30 formed in the tape sliding surface, it is possible to prevent the stray magnetic flux from being emanated from the one end of the magnetic gap g provided with the groove 30, thereby preventing side erasure otherwise caused by the stray magnetic flux.
Meanwhile, a tape streamer, as a recording and/or reproducing apparatus for recording and/or reproducing data with the use of a magnetic tape as a recording medium and also with the use of a rotary magnetic head device, is used for providing backup of data handled in an information processing unit, such as a computer. Since this sort of the recording and/or reproducing apparatus handles a large quantity of data, the data transfer rate needs to be raised in order to record and/or reproduce data promptly. For increasing the transfer rate, the frequency of the recording current needs to be raised. If the frequency of the recording current is increased, the current intensity of the recording current needs to be increased in order to acquire a recording output of a predetermined level. That is, the intensity of an optimum current for a recording output differs from one frequency to another.
For example, if the frequency of the recording current is 28 MHz, the recording current to recording output characteristics, shown in FIG. 2A, are demonstrated, with the optimum current value for a recording output being approximately 40 mAp-p. If the frequency of the recording current is 42 MHz, the recording current to recording output characteristics, shown in FIG. 2B, are demonstrated, with the optimum current value for a recording output being approximately 70 mAp-p and, if the frequency of the recording current is 56 MHz, the recording current to recording output characteristics as shown in FIG. 2C are demonstrated, with the optimum current value for a recording output being approximately 80 mAp-p.
With the magnetic head 50, used here, the depth length of the magnetic gap g is 10 μm.
That is, for increasing the frequency of the recording current and for recording data at a high transfer rate with optimum recording characteristics, it is necessary to use a large recording current.
On the other hand, in the recording and/or reproducing apparatus used for recording data handled in an information processing apparatus, it is a requirement to improve reliability as an apparatus as well as durability. In order to meet these requirements, the magnetic head used needs to be improved in durability. For improving the durability of the magnetic head, it is necessary to improve the abrasion resistance of the sliding surface, adapted for having sliding contact with the magnetic tape, and to enlarge the depth length of the magnetic gap g.
If the depth length of the magnetic gap g of the magnetic head is increased, the intensity of the recording current needs to be increased.
FIGS. 3, 4 and 5 show the recording current—recording output characteristics in case the frequency of the recording current is set to 28 MHz, 42 MHz and to 56 MHz, respectively, with the depth length of the magnetic gap g being 4 μm and 10 μm, respectively. In FIGS. 3 to 5, the recording current—recording output characteristics for the depth length of the magnetic gap g of 4 μm and 10 μm are denoted as D and E, respectively.
When data is recorded using the recording current with the frequency of 28 MHz, the magnetic head with the depth length of 4 μm exhibits characteristics shown in FIG. 3D, with the recording output optimizing current intensity being approximately 35 mAp-p, while the magnetic head with the depth length of 10 μm shows characteristics shown in FIG. 3E, with the recording output optimizing current intensity being approximately 40 mAp-p.
When data is recorded using the recording current with the frequency of 42 MHz, the magnetic head with the depth length of 4 μm shows characteristics shown in FIG. 4D, with the recording output optimizing current intensity being approximately 35 mAp-p, while the magnetic head with the depth length of 10 μm shows characteristics shown in FIG. 4E, with the recording output optimizing current intensity being approximately 70 mAp-p.
When data is recorded using the recording current with the frequency of 56 MHz, the magnetic head with the depth length of 4 μm shows characteristics shown in FIG. 5D, with the recording output optimizing current intensity being approximately 60 mAp-p, while the magnetic head with the depth length of 10 μm shows characteristics shown in FIG. 5E, with the recording output optimizing current intensity being approximately 80 mAp-p.
If, in the magnetic head, the depth length of the magnetic gap g is increased, the recording output optimizing current intensity is increased. In particular, when the frequency of the recording current is increased, the recording output optimizing current intensity is increased further.
With the discrete magnetic head 50, severed from the head block 1, shown in FIG. 1, the track width controlling groove 22 of the second magnetic core half block 20 intersects one lateral edge of the parallel groove 30 on the left side in FIG. 1 at a first point of intersection shown in FIG. 1. The metal magnetic film, forming the magnetic path as described above, is deposited in the track width controlling groove 22 lying at this first point of intersection F. It is noted that the unneeded stray magnetic flux is produced at and near this first point of intersection F, with the stray magnetic flux increasing with the intensity of the recording current.
When the recording track of the magnetic tape, on which the information signals have already been recorded in the magnetic gap g, traverses the first point of intersection F and its vicinity, demagnetization is produced under the influence of the stray magnetic flux emanated from the first point of intersection F and its vicinity. That is, demagnetization is produced in which the information signals already recorded in the recording track in the magnetic gap g are partially erased under the effect of the stray magnetic flux.
In particular, with the magnetic head in which the transfer rate of data to be recorded on the magnetic tape is increased or in which the depth length of the magnetic gap g is increased to improve durability, the intensity of the recording current needs to be increased, as described above. If the intensity of the recording current I is increased, the stray magnetic flux emanating from the first point of intersection and its vicinity is also increased. For example, if the intensity of the recording current I exceeds 50 mA, the noise level is increased due to demagnetization in which the information signals already recorded on the magnetic tape are partially erased by the stray magnetic flux emanating from the first point of intersection F and its vicinity, so that information signals cannot be recorded with optimum recording characteristics.